Compilare: user.c: In function ‘main’: user.c:25:9: warning: implicit declaration of function ‘strcat’ [-Wimplicit-function-declaration] strcat(A, buf); ^ user.c:25:9: warning: incompatible implicit declaration of built-in function ‘strcat’ [enabled by default] user.c:26:9: warning: implicit declaration of function ‘strlen’ [-Wimplicit-function-declaration] poz += strlen(buf); ^ user.c:26:16: warning: incompatible implicit declaration of built-in function ‘strlen’ [enabled by default] poz += strlen(buf); ^ user.c:27:9: warning: implicit declaration of function ‘strcpy’ [-Wimplicit-function-declaration] strcpy(buf,""); ^ user.c:27:9: warning: incompatible implicit declaration of built-in function ‘strcpy’ [enabled by default] user.c:33:5: warning: implicit declaration of function ‘strtok’ [-Wimplicit-function-declaration] p = strtok(buf," \n"); ^ user.c:33:7: warning: assignment makes pointer from integer without a cast [enabled by default] p = strtok(buf," \n"); ^ user.c:37:8: warning: incompatible implicit declaration of built-in function ‘strlen’ [enabled by default] if(strlen(p)>=7)return 0; ^ user.c:38:8: warning: incompatible implicit declaration of built-in function ‘strlen’ [enabled by default] if(strlen(p) == 6 && p[0]=='1' && p[1]=='1' && p[2]=='1')return 0; ^ user.c:39:20: warning: incompatible implicit declaration of built-in function ‘strlen’ [enabled by default] for(j = 0; j < strlen(p);j ++) ^ user.c:40:9: warning: implicit declaration of function ‘isdigit’ [-Wimplicit-function-declaration] if(!isdigit(p[j]))return 0; ^ user.c:41:5: warning: incompatible implicit declaration of built-in function ‘strcpy’ [enabled by default] strcpy(B,p); ^ user.c:49:18: warning: incompatible implicit declaration of built-in function ‘strlen’ [enabled by default] if(ok == strlen(B)) ^ user.c:21:10: warning: unused variable ‘a’ [-Wunused-variable] long a=0; ^ user.c:32:10: warning: ignoring return value of ‘fgets’, declared with attribute warn_unused_result [-Wunused-result] fgets(buf,100,pf); ^ In file included from /usr/include/stdio.h:934:0, from user.c:1: In function ‘fgets’, inlined from ‘main’ at user.c:32:10: /usr/include/i386-linux-gnu/bits/stdio2.h:253:2: warning: call to ‘__fgets_chk_warn’ declared with attribute warning: fgets called with bigger size than length of destination buffer [enabled by default]